This invention concerns a diaphragm spring friction clutch cover assembly of the type (hereinafter called "the type referred to") comprising a pressure plate, a cover, a diaphragm spring having a plurality of radially inwardly directed fingers, and said diaphragm spring acting between a first annular fulcrum arrangement on the pressure plate and a second annular fulcrum arrangement on the cover.
In use the assembly is secured to a driving member, for example a fly-wheel of a motor vehicle engine, so that a driven plate is clamped between the pressure plate and the driving member by the load of the diaphragm spring, the driven plate being released by an axial effort applied through a release bearing to radially inner ends of the fingers of the diaphragm spring.
In well known clutches comprising cover assemblies of the type referred to the driven plate is cushioned in that it comprises a carrier plate having friction facings mounted on cushioning between the facings. But to simplify and cheapen production of driven plates and to reduce inertia thereof, driven plates with reduced or no cushioning between the friction facings have been proposed. To compensate for this lack of cushioning it has been proposed to incorporate means which provides a degree of axial flexibility or cushioning into one of the annular fulcra. One way of providing the clutch cover assembly with cushioning means which is simple to manufacture and install and yet can provide a subjectively acceptable clutch engagement when mounted in a motor vehicle is disclosed in G.B. No. 1583403. That patent describes a diaphragm spring clutch cover assembly of the type referred to further comprising cushioning means in one of the annular fulcra arrangements, the cushioning means being formed by a single wavy ring having undulations which extend parallel to the axis of the diaphragm spring, and the undulations being constituted by a first series and by a second series of said undulations wherein the undulations of the first series have a lower stiffness but greater axial amplitude and wavelength than the undulations of the second series. During re-engagement of the driven plate (after a dis-engagement) the initial cushioning is by the first series and then by both series, which ensures that the clamp load increases progressively over a substantial range of movement of the release bearing during clutch re-engagement.
It has been found that in the mass production manufacturing of a wavy ring having undulations of differing stiffnesses and sizes it can be difficult to ensure consistency in the spring characteristics of the wavy rings.
An object of this invention is to provide a diaphragm spring clutch cover assembly of the type referred to capable of being constructed, as will be understood from the ensuing description with reference to the drawings, in which the aforesaid difficulty may be avoided and at the same time that assembly can be used to form a clutch for a motor vehicle in which clutch engagement is subjectively acceptable and the clamp load increases progressively during re-engagement